Method and apparatus for determining shear force between the wafer head and polishing pad in chemical mechanical polishing

ABSTRACT

A method for (a) determining the shear force between a wafer head and a polishing pad in a polishing tool using a CMP polishing tool with a plate above the wafer head which hangs or rests on the plate. The plate is connected to the CMP polishing tool by (b) low friction motion means (c). A load cell sensor is fixed to the framework of the polishing tool or another immovable structure. (d) The load cell determines the force from the leading edge of the plate when the wafer head is in contact with the polishing pad. (e) Signals from the load cell sensor reporting the shear force. A CMP polishing tool which includes elements corresponding to each of points (a)-(e) in the above method.

FIELD OF THE INVENTION

The present invention relates to a Method and Apparatus for determining shear force between the wafer head and polishing pad in chemical mechanical polishing (CMP) and from that further calculating the coefficient of friction (COF) between the wafer and polishing pad.

BACKGROUND OF THE INVENTION

The present invention is a method and a CMP tool for determining the shear force between the wafer head and the polishing pad wherein the said determination is accomplished by means of a CMP polishing tool with a plate positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, said plate connected to the framework of the said CMP polishing tool by low friction motion means capable of sliding in a direction perpendicular to the line between the center of the polishing pad and the center of the wafer head, and a load cell sensor firmly fixed to the framework of the polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of said plate when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals thus obtained reporting the shear force.

The present invention is also a method and CMP polisher that determine two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of a CMP polishing tool with two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the polishing tool by low friction motion means, the other said plate connected to the first said plate by low friction motion means allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, and load cell sensors firmly fixed to the framework of the polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the vector sum of the said signals reporting the shear force.

The present invention further is a method and CMP polishing tool that determine two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of a CMP polishing tool with two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the polishing tool by low friction motion means, the other said plate connected to the first said plate by low friction motion means allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, and load cell sensors firmly fixed to the framework of the polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the vector sum of the said signals reporting the shear force device for determining two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the polishing tool by low friction motion means, the other said plate connected to the first said plate by low friction motion means allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, and load cell sensors firmly fixed to the framework of the polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the vector sum of the said signals reporting the shear force.

Chemical Mechanical Polishing (CMP) polishing tools, wafer heads, polishing pads and diamond conditioner disks form the key components of the equipment used to carry out CMP processes in recent years. These various pieces of equipment have been produced and marketed by several vendors to standards of reliable quality and effectiveness. The function of the slurry is to deliver continuously the mechanical abrasive particles and chemical components to the surface of the wafer and to provide a means of removing reaction products and wafer debris from the polishing surface. The function of the polishing pad is to abrade the surface of the wafer during polishing in concert with the slurry. The polishing pad is typically made of polyurethane or a substance of similar properties and the surface is roughened to enhance its effectiveness as a polishing surface for the wafer. It is positioned face up both to hold the slurry and to facilitate and is rotated from below. The surface of the polishing pad is usually provided with long grooves that serve both to assist in the dispersion of slurry under the wafer head during polishing and to provide effective removal of spent slurry and wafer detritus which are typically swept off of the pad by centrifugal force as the pad rotates. The pad rotates at a rate of typically about 20 to 100 RPM

The diamond conditioner discs serve the purpose of continual and consistent roughening of the polishing pad and are suspended from an arm or a bridge, platform or similar structure of the polishing tool so that they are pressed diamond bearing face down into the polishing pad. Diamonds on the conditioner disc surface cut and roughen the pad during CMP operation. This is necessary because the action of the slurry on the wafer and pad quickly smoothen the pad otherwise greatly diminishing its effectiveness and the rate of removal of the wafer surface during polishing. The diamond conditioner disk sits under a load on the polishing pad and is both rotated and moved back and for the between the center of the pad to ensure an even dispersal of roughening over the polishing pad. The wafer head consists of the wafer and the apparatus for supporting and rotating the wafer and is hung from a supporting arm, bridge, platform or similar structure of the polishing tool and holds the wafer face down on the face of the polishing pad while rotating it.

Depending upon the type of wafer to be polished and the specific objectives of the operator, a variety of loads, respective rotation rates and, in the case of the diamond conditioner disc, motions across the polishing pad surface may be employed. Likewise, the type, quantity and concentration of slurry may be varied to obtain various results. Of great concern to all operators in the rate at which the various components of the CMP polishing apparatus will remove the surface material of the wafer. There are many reasons for this of course. One is diagnostic. A too slow or too fast removal rate may be indicative of failure or improper selection or setting of one of the components described above. However determination of the wafer surface cutting rate is difficult to observe during the operation of the CMP polisher (which typically requires about one minute per wafer operation time). It has long been understood that the coefficient of friction of a two surface system bears a roughly proportional relationship to the rate at which inflexible material is removed in a surface to surface interaction. It is not possible to determine the rate directly from the coefficient of friction, however, if in a particular system, certain rates of removal are consistently associated with certain coefficients of friction, then the coefficient of friction value and its change over time can be diagnostic of the performance of the system and other effects as well.

The coefficient of friction is calculated by dividing the shear force (force in the direction of motion of one of the surfaces relative to the other) by the downforce (vertical force pressing down).

COF=F_(s)/F_(d)

Where F_(s) is shear force and F_(d) is down force.

The shear force is preferably horizontal for CMP purposes but it is not essential that it be so. In the CMP system, there are two major shear forces, the shear force between the wafer head and the polishing pad and the shear force between the diamond conditioning disc and the polishing pad. The shear force for the wafer head or diamond conditioner disc can be measured using a load cell contacting the bearing casing of the rotation axle thereof, said load cell oriented opposite to the direction of rotation of the polishing pad at a point where the line from the center of the polishing pad through the center of the wafer head or diamond conditioning disc intersects the edge of the polishing pad. Of course a measurement of the shear force could be made on the polishing pad but it would be composed of unresolved components of shear force from the wafer head and the diamond conditioner and the direction of the force would have to be indentified.

PRIOR ART

Methods of the prior art have placed the load cells for determination of shear force beneath the module of the polishing pad within the CMP polishing tools or have been so narrow as not to provide a stable directional determination of the shear force based on the force on the shaft bearing of the shaft for turning the wafer head. This allowed a number of other components to be included in the final numerical value of magnitude of force component and generally created a lower and at times undesirable degree of inaccuracy and difficulty in consistent analysis and reporting of shear force and COF.

HOW THE PRESENT INVENTION OVERCOME THE PROBLEMS OF THE PRIOR ART

The present invention overcomes the problems of the prior art by means of a highly sensitive and efficient structure comprising one plate capable of sliding in a direction perpendicular to the line between the center of the polishing pad and the center of the wafer head connecting to a load cell on its leading edge. A further embodiment of the present invention overcomes the problems of the prior art with two plates, one on sliding means attached to the tool and the other on sliding means oriented perpendicular to the sliding means of the first place and both plates attached to load cells on their leading edge. The present invention in all of its embodiments allows resolution of the shear force into measurable components. Additionally, the present invention, by suspending the wafer head and its rotational and supporting apparatus from the plates, greatly limits or eliminates the effects on the determination of shear force of any but the forces that actually work upon the head. Finally, the two plate embodiment of the present invention, by resolving all force on the bearing of the axle of the head into perpendicular components, allows simple and accurate acquisition of the shear force regardless of its precise orientation.

SUMMARY OF THE INVENTION

The present invention is a method and a device, specifically a CMP polishing tool, that determines the shear force between the wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of a CMP polishing tool with a plate positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, said plate connected to the framework of the CMP polishing tool by low friction motion means capable of sliding in a direction perpendicular to the line between the center of the polishing pad and the center of the wafer head, and a load cell sensor firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of said plate when the CMP polishing tool is in operation and the wafer head is in contact with the CMP polishing pad, the signals thus obtained reporting the shear force.

The present invention is also a method and CMP polishing tool for determining two perpendicular force components of shear force between a wafer head and the polishing pad wherein the said determination is accomplished by means of two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the CMP polishing tool by low friction motion means, the other said plate connected to the first said plate by low friction motion means allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, and load cell sensors firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the CMP polishing tool is in operation and the wafer head is in contact with the polishing pad, the said signals reporting the perpendicular components of shear force.

The present invention also more particularly is a method and CMP polishing tool that determines two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the said CMP polishing tool by low friction rails, the other said plate connected to the first said plate by low friction rails allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, load cell sensors firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals of said load cells reporting the components of shear force, 4 load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, which generates a signal from the said load cells at the bottom of the CMP polishing tool and the down force and perpendicular shear force signals are reported and the signals from the load cells are delivered to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and calculates and reports the coefficient of friction between the wafer and the polishing pad

The method and CMP polishing tool of the present invention may be supplemented by addition of load cells at the bottom of the CMP polishing tool for the purpose of determining the load on the wafer head and thereby making possible determination of the down force for purposes of calculating the COF between the wafer head and the polishing pad. Another particularly attractive feature of the invention is the suitability of routing the signals from the various load cells to a data processing unit where with, software designed for that purpose, numerical or graphic values of the components of shear force and down force data, and the change in these values of these over time can be reported and the calculation of COF and other relevant statistical quantities can be calculated in real time. It is even possible to provide a feedback loop to adjust load or rotation speed of the wafer head or polishing wheel in response to changes in any of these data or calculated figures.

The CMP polishing tool of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available CMP shear force determination and COF calculation methods and CMP polishing tools. Thus, it is an overall objective of the present invention to provide modified CMP polishing tools and methods of using them that remedy the shortcomings of the prior art.

The purpose of these CMP polishing tools and the methods of their use are to allow more effective determination and reporting of shear force and calculation of COF during CMP.

Manufacturers and users of polishing pads, wafers and CMP polishing tools need to know the Shear force and COF values of the wafer head-polishing pad interface in real time and to be able to see how these change over time. This allows manufacturers to improve the properties of wafers, polishing pads and CMP polishing tools and to locate and overcome defects thus allowing users to optimize their use of a given wafer or polishing pad type or CMP polishing tool.

BRIEF DESCRIPTION OF THE DRAWINGS

Following is a brief description of the drawings explaining the present invention:

FIG. 1 is an overhead view of the CMP polishing tool and basic components of CMP.

FIG. 2 is a side view of the CMP polishing tool and basic components of CMP.

FIG. 3 is a side view depiction of the single plate embodiment of the present invention

FIG. 4 is a side view depiction of the two plate embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in two embodiments a method and CMP polishing tool for determining shear force in CMP is provided.

Through the application of the method of the present invention and the use of the CMP polishing tool of the present invention, the determination of shear force between the wafer head and polishing pad in CMP may be rapidly carried out with a minimum of error inducing effects. Furthermore, the present invention may be easily and cost-effectively applied to facilitate and enhance CMP polishing tools and components used therein. These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

All dimensions for parts in the present invention follow are based on a pad size of about 20″ to 30″ in diameter and a wafer size of between 8″ and 12″ in diameter and may be altered as needed in proportion to changes in the size of the polishing pad and wafer used. The specific dimensions given herein are in no way limiting but are by way of example to demonstrate an effective embodiment of the invention.

The present invention is both a shear force determination method carried out using a CMP polishing tool and a standard CMP polishing tool modified to carry out that method. The CMP polishing tool of the present invention (10) may be any CMP polishing tool presently in use today but rotary type tools are preferred. The CMP polishing tool of the present invention possesses a wafer head (12) and its supporting and rotation apparatus (14), a diamond conditioner disc (16) and its supporting, rotation and oscillation apparatus (18), a polishing pad (20) and its platen (22) and supporting and rotating apparatus (24), the module of the polishing pad within the framework of the CMP polishing tool (25) a water and slurry source (26) and a bridge or platform structure (28) on which the wafer head supporting and rotation apparatus (14) may rest and in some cases upon which the diamond conditioner disc supporting, rotation and oscillation apparatus (18) may also rest.

The wafer head (12) of the present invention may be any wafer head that can hold a CMP wafer (30). The wafer (30) may be, without limitation, any semiconductor wafer and silicon dioxide covered, copper covered, tungsten covered and any other metal or dielectric covered wafers may be used. The size of the wafer of the present invention (30) is not particularly limited but wafers from 8 to 12 inches in diameter are preferred. The rotation rate of the wafer of the present invention (30) is not particularly limited but a rotational rate of 20 to 100 RPM is preferred.

As the polishing pad (20) of the present invention, any polishing pad used in CMP polishing may be used. The polishing pad (20) may be made of any material with a suitable hardness and a pad made of polyurethane is preferred. The diameter of the polishing pad is not particularly limited but polishing pads 20 to 32 inches in diameter are preferred. Rotation rate of the polishing pad (20) is not particularly limited but a rate 20 and 100 RPM is preferred. The polishing pad (20) may be flat or it may be inscribed with concentric and radial grooves to conduct slurry. The polishing pad (20) of the present invention rests on a platen (22) that may be either fixed or removable. The platen may be any platen commonly used with the CMP polishing Tool (10) or designed for use thereupon.

The diamond conditioner discs (16) of the present invention are not particularly limited and, any commercially available or developmental diamond conditioner discs presently used in CMP polishing may be used. The diameter of the diamond conditioner disc (16) is not particularly limited but and diamond conditioner discs with diameters 4 inches may be used. The rate of rotation of the diamond conditioner disc (16) is not particularly limited but rates of 30 to 105 RPM are preferred. The rate of oscillation of the diamond conditioner disc (16) between the center and edge of the polishing pad (20) is not particularly limited but rates 5 to 20 oscillations per minute are preferred. The load on the diamond conditioner disc (16) is not particularly limited and loads between 0 and 11 pounds are preferred. The diamond conditioner disc supporting, rotation and oscillation apparatus (18) of the present invention may be, without limitation, any supporting, rotation and oscillation apparatus suitable for use with the CMP polishing tool (10) used.

As the slurry of the present invention (26), without limitation, any commercial slurry or slurry developed for CMP processes may be used and more particularly slurries based on silica, alumina and ceria particles may be preferably used. As the means of introducing the slurry (26), any suitable means of introducing slurry to the polishing pad (20) surface without limitation may be used including without limitation Tygon® tubes for both slurry and wash water.

As the plates of the present invention any plates may be used that are capable of supporting the weight of the support and rotation apparatus of the wafer head of the present invention (14) and the wafer (30) and wafer head (36) and are still able to move unrestrictedly in the indicated direction, but metal plates are preferred and steel plates are more preferred. It is a singular point of the present invention that the plate or plates only support the wafer (30), wafer head (12) and wafer head support and rotation apparatus (14) and not additional structures capable of introducing extraneous components of shear force such as the diamond conditioner disc (16) and its rotation and oscillation apparatus (18) as was the case in the methods and devices of the prior art. As to the thickness of the plates of the present invention there is no particular limitation but the thickness should not be so large as to make the plates too massive to utilize easily or so thin that the weight they are carrying or the forces they bear will deform them. A thickness of ⅛ inch to ½ inch is preferred and ¼ inch steel plate is more preferred. The lateral dimensions of the plates are not particularly limited but should be large enough to support the supporting and rotation apparatus of the wafer head of the present invention (14) and not so large as to interfere with operation of the CMP polishing tool (10) or access to other working parts thereof. Dimensions between 8 inches and 16 inches in width and eight inches and 2 feet in length are preferred.

The location of the plates of the present invention is above the wafer head but is otherwise not particularly limited. They may rest on or hang from on a bridge structure, platform structure or other support structure attached to the structure of the CMP polishing tool or some other immovable structure; however, it is preferred that they be attached to a structure that is attached to the framework of the CMP polishing tool and attachment on top of the bridge or platform structure of the present invention is more preferred (28). The orientation of the attachment of the plates is not particularly limited but level horizontal attachment is preferred.

In the single plate embodiment of the present invention, the direction of the plate in which the motion of the single plate (32) is possible and therefore the orientation of the plate parallel to the direction of motion of the polishing pad (20) under the center of the wafer head (14). Another way of expressing this is to say that the direction of freedom of motion of the plate (32) is perpendicular to the line between the center of the wafer head (12) and the center of the polishing pad (20). If this is not the case to a reasonably precise degree, an accurate reading of the shear force between the wafer head (30) and the polishing pad (20) is impossible to measure directly with any accuracy because a significant component of the force will be in a direction in which the plate (32) is not free to move and will not be measured by the load cell sensor (34) contacting the plate (32). The advantage of this embodiment, however, is that it is much simpler to prepare and execute and if the direction of the plate is accurately determined and set above the wafer head (12), for practical purposes almost the entire magnitude of the shear force is expressed.

In the double plate embodiment of the present invention, the directions in which the respective plates are free to move may theoretically be any direction in which both plates are aligned with some component of the forward motion of the polishing pad (20) at the point under the center of the wafer head (12) as long as the plates are in a perpendicular orientation to each other. The reason for this is that with when two perpendicular components in the same plane in which a force is expressed are known, it is always possible to determine both the magnitude and direction of the force. The advantage of this embodiment of the present invention is that it always provides the entire magnitude of the shear force between the wafer (30) and the polishing pad (20) regardless of whether the direction of the plates in regard to the direction of motion of the polishing pad (20) under the central point of the wafer head (12). However, the arrangement where one the direction of the freedom of motion of one plate is perpendicular to the wafer head (12) center to polishing pad (20) center line is preferred].

The supporting apparatus of the wafer head of the present invention is not particularly limited but shall comprise the motor (36) for turning the shaft (38) that rotates the wafer head (12), the gears and shafts (not shown) for transferring power to the shaft (38) of the wafer head (12) and the bearings (not shown) and bearing casing (40) thereof and any power or signal cables (42) and control units (not shown) attached thereto. The means of fastening the supporting and rotation apparatus of the wafer head (14) is not particularly limited and may be any suitable means used to fasten devices of this type, however bolting the devices to the single plate (32) for the single plate embodiment or the outermost plate (44) from the Framework of the CMP polishing tool (10) in the double plate embodiment is preferred.

The means of fastening the plates of the present invention to the Framework (11) of the CMP polishing tool (10) of the present invention is not particularly limited. However, the plates may be fastened to the CMP polishing tool framework (10) of the present invention either directly or indirectly. The meaning of directly is that the means of low friction motion of the present invention (48) are attached directly to the structure of the CMP polishing tool of the present invention by any suitable means such as bolting them, welding them or incorporating them into the surface of the CMP polishing tool framework (11) and, in turn, the single plate (32) in the case of the single plate embodiment or the plate closest (46) to the Framework (11) of the CMP polishing tool (10) in the case of the two plate embodiment rests, rides or hangs as the case may be on the means of low friction motion of the present invention (48). The meaning of indirectly is that the said means of low friction motion of the present invention (48) for the single plate (32) in the case of the one plate embodiment or the plate closest (46) to the Framework (11) of the CMP polishing tool in the case of the two plate embodiment is affixed not directly to the structure of the CMP polishing tool but to another plate or device (50) attached to the Framework (11) of the CMP polishing tool (10). The method of affixation is not particularly limited and may include without limitation bolting, clamping, welding but although clamping is may allow later easy directional adjustment of the plates bolting is preferred for since it is stronger while leaving some possibility for adjustment later on. Of course it is contemplated that in manufacturing the CMP polishing tool (10), the plate or device holding the low friction motion means (48) may be incorporated into the framework (11) of the CMP polishing tool (10) itself.

The manner of fastening or affixing the low friction motion means (48) to the plate or device (50) attached to the CMP polishing structure is not limited and may be any suitable means given the type of low friction motion means employed and includes he methods used in the attachment of the low friction motion means (48) to the framework (11) of the CMP polishing tool (10).

The low friction means of the present invention (48) and, where applicable, the plate or device (50) attached to the framework (11) of the CMP polishing tool (10) must be attached securely so that there is no appreciable motion of them with respect to the framework (11) of the CMP polishing tool (10) or where a plate or device (50) are used between the low friction motion means (48) and the said plate or device (50) as well.

The framework (11) of the CMP polishing tool (10) shall be the outer substantial metal and other structural material derived housing of the CMP polishing tool (10) together with anything permanently or structurally attached to it in such a way that there is effectively no motion or slippage between such structurally attached item and the said metal housing except as otherwise expressly and more specifically described herein.

In the double plate embodiment of the present invention, the low friction motion means (48) by which the two plates are connected shall be the means of connection of the plate closest (46) to the framework (11) of the CMP polishing tool (10) to outermost plate (44) from the framework (11) of the CMP polishing tool (10) and these low friction motion means (48) are not particularly limited. However, the low friction motion means (48) in each case should be suitable for the location and position of the plates supported, whether riding or hanging, and should be strong enough to bear the load of the plates and what they support with no appreciable effect on the friction generated by motion along them. The low friction motion means (48) of the present invention should be linear and preferably should run or encompass the length of the plate or plates to which it is attached. Block and Pillow attachments or low friction rail systems are preferred and low friction rail systems are more preferred where the wafer head support and rotation apparatus (14) rests on top of the single plate (32) or the outermost plate (44) from the framework (11) of the CMP polishing tool (10) as the case may be.

Low friction motion means (48) as used in the present invention are not particularly limited but it is preferred that such motion means generate a total frictional force in response to motion of the plates of 20 lbf or less and more preferably 10 lbf or less.

The load cell sensors contacting the plates (34) of the present invention may be any load cell sensors of suitable capacity to measure the shear force of the present invention and preferably 0 to 225 lbf force are used.

The load cell sensors contacting the plates (34) of the present invention may positioned at any point along the leading edge of the plates. More than one load cell sensor may be used on any leading edge but one load cell sensor per leading edge is preferred. The load cell sensors shall be affixed to protrusions, fixtures or other structures (52) incorporated into or part of the framework (11) of the CMP polisher (10). The operator should be careful in placing the plates to ensure that the support structures (52) for the plate load cell sensors (34) are present or may easily be added.

The load cell sensors contacting the plates (34) of the present invention may be attached by electrical wiring (54) or other transmission means such as wireless communication to a data readout means (not shown) or a data processing means (not shown), however electrical wiring is preferred and connection to data processing means is preferred.

The data processing means of the present invention are not particularly limited and may be any data processing means suitable for receiving, analyzing, storing, reporting and using the data from the load cell sensors in further calculations as well as in feedback applications such as adjustment of the rate of rotation of the polishing wheel or wafer head.

The data of the present invention is electronic signal data from load cells representing the amount of force exerted against them by the leading edges of the plates of the present invention. Additionally the data of the present invention may include electronic signals from load cell sensors (56) positioned under the CMP polishing tool, the change in which load during the operation of the CMP polishing tool (10) represents the z-force or down force that may be used in calculation of the coefficient of friction between the wafer head (30) and the polishing pad (20).

The reports of the present invention are not particularly limited and may without limitation be any report of raw data from the load cells or processed data from the data processing means showing shear force, down force, change in these values over time and calculated COF values or mathematical and particularly statistical analyses of any of these. Reports may be displayed numerically or graphically on a dial or on a screen and may be stored or output using any applicable storage or output media.

In addition load cell sensors (56) may be attached to the bottom of the module of the polishing pad (25) within the framework (11) of the CMP polisher tool to obtain information on the down force or z direction force. The module of the polishing pad (25) within the framework (11) of the CMP polishing tool should not be directly structurally connected to the framework (11) of the CMP polishing tool (10) itself as this would render measurement of the z direction or down force impossible.

The load cell sensors (56) determine down force on the wafer head (30) by measuring the load before and after application of the wafer head (30) to the polishing pad (20) and reporting the data from which the difference can be calculated to determine the said down or z direction force. This information can be used independently or in the calculation of the COF between the wafer head (30) and the polishing pad (20). The type of load cell sensors used to determine the z direction or down force of the present invention is not particularly limited, however, the load cell sensors must be of a type sufficiently durable to bear the weight of the CMP polishing tool and at the same time sensitive enough to register with reasonable accuracy the change in y force when the wafer head is engaged to the polishing pad. The number of load cells is not particularly limited and one or more load cells may be used. If more than one load cell is used and the cells are arrayed in a geometric pattern it should be possible to obtain variations in the z force over the polishing pad. Four load cells (56) at the corners of the bottom of the module of the polishing pad (25) within the framework (11) of the CMP polishing tool (10) are preferred.

The load cell sensors (5) used to measure the z direction force of the present invention may directly support the module of the polishing pad (25) within the framework (11) of the CMP polishing tool (10) or they may support a plate or other device that supports the module of the polishing pad within the framework (11) of the CMP polishing tool. Where 3 or fewer load cells (56) are used to support the module of the polishing pad within the framework (11) of the CMP polishing tool, the use of a plate (not sown) is preferred and may be accompanied by low friction motion supports (not shown). Where four or more load cells are used to support the module of the polishing pad within the framework (11) of the CMP polishing tool (10), either the load cells may directly support the base of the module (25) or a plate (58) may be used.

PRACTICE EXAMPLES Example 1 Single Plate

An APD 500 polisher with a bridge over the polishing pad module area was equipped with 2 low friction rails along its length for 15 inches and upon these rails was laid a ¼ inch steel plate with attachments to allow the plate to slide freely along these rails. The bridge was split in the middle to allow the shaft of the wafer head to descend through it to the wafer head itself and the plate was also provided with a hole to allow the shaft to pass through it and the opening in the bridge. To the top of the plate was attached the wafer head support apparatus by bolting them fast. A strain gauge load cell sensor was attached in front of the leading edge of the plate and fixed to a support fixture bolted onto the vertical wall of the bridge below the point where the load cell contacted the leading edge of the plate.

Four strain gauge load cell sensors were placed under the corners of the module of the polishing pad within the framework of the CMP polishing tool. The signal leads from the load cell sensor on the bridge of the framework of the CMP polishing tool and the load cell sensors under the module of the polishing pad within the framework of the CMP polishing tool are relayed through a an individual amplifier for each load cell sensor and from there to a relay board. The amplifiers and relay board were within the control structure of the CMP polishing tool. From there the signals were combined and output through the USB port of a laptop PC computer which was programmed with data for distinguishing, measuring and outputting the signals and calculating shear force, down force and COF which are then be presented in either numeric or graphic form in real time.

A 200-mm blanket oxide wafer was fixed to the wafer head and rotation was set at 93 RPM and the load on the wafer head was set so that the processed output from the load cell sensors registered at 3 PSI. Cerium oxide slurry was used to polish 200-mm blanket oxide wafers. Slurry flow rate was set at 200 ml/min. A 100-grit diamond conditioner disc manufactured by Mitsubishi Materials Corporation was equipped and operated at 30 RPM and 16 sweeps per minute at 5.8 PSI load. The polishing pad was an RHEM IC 1000 A2 k-groove pad at 3 PSI and 1.37 m/s and polishing was carried out for 1 minute. Shear force and down force were measured in real-time at a sampling frequency of 1,000 Hz. The average down force was 145 lbf and the average of the shear force was 62.1 lbf. The coefficient between the wafer and the polishing pad was determined to be 0.428.

Example 2

Except that an APD 800 CMP polishing tool was used and that atop the first plate described in Example 1, 2 low friction rails were attached by bolting them to the lower plate in the direction perpendicular to the direction of motion of the lower plate. An additional plate with fixtures to allow it to ride on the said rails and an opening corresponding to the opening in the bridge and the lower plate was set upon the rails on the lower plate and the wafer head supporting apparatus was attached to the top of the upper plate in the same manner it had been attached to the top of the lower plate in Example 1. A strain gauge load cell sensor was attached to the framework of the CMP polishing tool and contacted the outermost plate from the framework of the CMP polishing tool in the direction of forward motion of that plate. The signal lead from this load cell sensor was joined to the others in the relay and amplified and relayed to the computer as in Example 1.

A 300-mm blanket oxide wafer was fixed to the wafer head and rotation was set at 51 RPM and the load was set at 1 PSI. A 100-grit diamond conditioner disc was equipped and operated at 90 RPM and 10 oscillations per minute at 7 lbf load. The polishing pad was rotated at 10 RPM and polishing was carried out for 1 minute. The average down force was 109 lbf and the average shear force was 68.9 lbf. The coefficient of friction between the wafer and the polishing pad was determined to be 0.632.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overhead view of the CMP polishing tool and basic components of CMP.

10 is the entire CMP polishing tool.

11 is the framework of the CMP polishing tool

12 is the wafer head

14 is the supporting and rotational apparatus of the wafer head

16 is the diamond conditioner disc

18 is the rotational and sweeping apparatus of the diamond conditioner disc

20 is the polishing pad

26 is the slurry and water source

28 is the bridge or platform structure of the CMP polishing tool.

32 is the single plate of the single plate embodiment

34 is the load cell contacting the plate

36 is the motor for turning the shaft that rotates the wafer head

38 is the shaft that rotates the wafer head

40 is the bearing casing of the shaft that rotates the wafer head

42 are power or signal cables

52 are support structures for the load cell sensors

54 are electrical wiring for the load cell sensors

FIG. 2 is a side view of the CMP polishing tool and basic components of CMP. Except as below all numbering is the same as above where applicable.

22 is the polishing pad platen

24 is the supporting and rotational apparatus of the polishing pad

30 is the wafer

48 is the means of low friction motion

56 are load cell sensors for the down force

FIG. 3 is a side view depiction of the single plate embodiment of the present invention. All numbering is as in the preceding figures.

FIG. 4 is a side view depiction of the two plate embodiment of the present invention.

44 is the outermost plate from the framework of the CMP polishing tool.

46 is the plate closest to the framework of the CMP polishing tool.

50 is the plate or device for low friction means attachment

The effectiveness of the present invention. The present invention has the effect of greatly increasing the simplicity, accuracy and precision of measurement of the shear force between the wafer head and the polishing pad in CMP polishing processes and as a consequence the determination of COF which can be used to determine many kinds of useful information as to the condition of the head and how effectively a process on a wafer is being carried out. 

1. A method for determining the shear force between the wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of a CMP polishing tool with a plate positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, said plate connected to the framework of the said CMP polishing tool by low friction motion means capable of sliding in a direction perpendicular to the line between the center of the polishing pad and the center of the wafer head, and a load cell sensor firmly fixed to the framework of the polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of said plate when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals thus obtained reporting the shear force.
 2. A method according to claim 1 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the shear force.
 3. A method according to claim 1 wherein load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, and the down force and shear force thus obtained may be used to calculate the coefficient of friction between the wafer head and the polishing pad.
 4. A method according to claim 3 wherein the number of load cells measuring the down force is
 4. 5. A method according to claim 3 or 4 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and reports and calculates the coefficient of friction between the wafer and the polishing pad.
 6. A method according to claim 1 wherein the said low friction motion means are rails.
 7. A method according to claim 1 wherein the said low friction motion means are block and pillow sliders.
 8. A method for determining two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of a CMP polishing tool with two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the polishing tool by low friction motion means, the other said plate connected to the first said plate by low friction motion means allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, and load cell sensors firmly fixed to the framework of the polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals from said load cells reporting the perpendicular components of shear force.
 9. A method according to claim 8 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the respective perpendicular components of the total shear force.
 10. A method according to claim 8 wherein load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, and the down force and shear force thus obtained may be used to calculate the coefficient of friction between the wafer head and the polishing pad.
 11. A method according to claim 10 wherein the number of load cells used to determine the down force is
 4. 12. A method according to claim 10 or 11 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and reports and calculates the coefficient of friction between the wafer and the polishing pad.
 13. A method according to claim 8 wherein the said low friction motion means are rails.
 14. A method according to claim 8 wherein the said low friction motion means are block and pillow sliders.
 15. A CMP polishing tool that determines and reports the shear force between the wafer head and the polishing pad wherein the said determination is accomplished by means of a plate positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, said plate connected to the framework of the CMP polishing tool by low friction motion means capable of sliding in a direction perpendicular to the line between the center of the polishing pad and the center of the wafer head, and a load cell sensor firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of said plate when the CMP polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals thus obtained reporting the shear force.
 16. A CMP polishing tool according to claim 15 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the shear force.
 17. A CMP polishing tool according to claim 15 wherein load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, and the down force and shear force thus obtained may be used to calculate the coefficient of friction between the wafer head and the polishing pad.
 18. A CMP polishing tool according to claim 17 wherein the number of load cells measuring the down force is
 4. 19. A CMP polishing tool according to claim 17 or 18 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and reports and calculates the coefficient of friction between the wafer and the polishing pad.
 20. A CMP polishing tool according to claim 15 wherein the said low friction motion means are rails.
 21. A CMP polishing tool according to claim 15 wherein the said low friction motion means are block and pillow sliders.
 22. A CMP polishing tool that determines and reports two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the CMP polishing tool by low friction motion means, the other said plate connected to the first said plate by low friction motion means allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, and load cell sensors firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the CMP polishing pad, and reports the said perpendicular force components as signals.
 23. A CMP polishing tool according to claim 22 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the respective perpendicular components of the total shear force.
 24. A CMP polishing tool according to claim 22 wherein load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, and the down force and shear force thus obtained may be used to calculate the coefficient of friction between the wafer head and the polishing pad.
 25. A CMP polishing tool according to claim 24 wherein the number of load cells measuring the down force is
 4. 26. A CMP polishing tool according to claim 24 or 25 wherein the load cells are attached to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and reports and calculates the vector sum of the said two perpendicular components and the COF between the wafer and the polishing pad.
 27. A CMP polishing tool according to claim 22 wherein the said low friction motion means are rails.
 28. A CMP polishing tool according to claim 22 wherein the said low friction motion means are block and pillow sliders.
 29. A method for determining two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means of a CMP polishing tool two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the said CMP polishing tool by low friction rails, the other said plate connected to the first said plate by low friction rails allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, load cell sensors firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals of said load cells reporting the components of shear force, 4 load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, which generates a signal from the said load cells at the bottom of the CMP polishing tool and the down force and perpendicular shear force signals are reported and the signals from the load cells are delivered to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and calculates and reports the coefficient of friction between the wafer and the polishing pad.
 30. A CMP polishing tool that determines two perpendicular force components of shear force between a wafer head and the polishing pad in a polishing tool wherein the said determination is accomplished by means two plates positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of the said CMP polishing tool by low friction rails, the other said plate connected to the first said plate by low friction rails allowing the said other plate to slide in a direction perpendicular to the motion of the first said plate, load cell sensors firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of each of said plates when the polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals of said load cells reporting the components of shear force, 4 load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the down force, which generates a signal from the said load cells at the bottom of the CMP polishing tool and the down force and perpendicular shear force signals are reported and the signals from the load cells are delivered to a data processing means that receives and analyzes the data and reports the respective components of and the total shear force and calculates and reports the coefficient of friction between the wafer and the polishing pad 